In radio communication systems, signal-to-noise ratio (SNR) has heretofore been widely used as a measure to indicate the receiving quality of a radio signal received by a reception device from a transmission device.
In a radio communication system, the amplitude and phase of a radio signal vary due to characteristics of a radio channel (e.g., frequency response characteristic) in addition to the influence of noise. For this reason, for accurate measurement of an SNR, it is important to remove the varied portion of the radio signal caused by the characteristics of the channel, and then calculate noise power.
In addition, the following technique has been proposed as an SNR measurement technique applicable to a multicarrier scheme using a number of sub carriers (see Patent Document 1).
The reception device described in Patent Document 1 receives a radio signal from a transmission device via a radio channel and estimates an SNR by using a first known signal and a second known signal included in the received radio signal. The first known signal and the second known signal here are signals whose signal pattern (e.g., an M sequence, a Walsh sequence, or the like) is known by the reception device. Moreover, the second known signal is disposed continuously after the first known signal in the time direction.
The reception device described in Patent Document 1 calculates the first known signal's channel estimation information indicating estimation of characteristics of the channel, and multiplies the second known signal by the calculated channel estimation information. The reception device then calculates noise power on the basis of the difference between the second known signal after the multiplication by the channel estimation information and the second known signal before the multiplication by the channel estimation information.    Patent Document 1: Japanese Patent No. 3455773 ([Claim 1], FIG. 3)